Youth in the juvenile justice system (JJS) are at substantial risk for HIV due to numerous individual and contextual risk factors (e.g. family, peers, neighborhood). Yet there are few interventions designed to address their substantial profile of risk. The Investigator's long-term career goals are to become an independent researcher dedicated to developing and evaluating HIV/STI interventions that address the larger context of risk for the most vulnerable youth (e.g. JJS youth). This K01 Award application focuses on building the Investigators research skills necessary to work with the probation system community (i.e. youth on probation, caregivers and probation staff) to develop, implement, and pilot test of a family-based HIV/STI intervention. All activities will be mentored by a multidisciplinary team of NIH-funded researchers who together have decades of experience in understanding contexts of HIV risk, working within the JJS, and developing family-based HIV prevention interventions for high risk youth. Embedded in an NIMH research center devoted to reducing and preventing HIV for over 20 years, the HIV Center of Clinical and Behavioral Research, the PI will have access to the Center's resources, research cores, and scientific faculty to accomplish four training objectives that have been developed in close consultation with the PIs mentors: 1) strengthen knowledge of ecological theories of behavior change and empirically validated approaches associated with family-based HIV/STI prevention interventions for high risk youth; 2) learn theoretical principles and methods of community-based research that will be used to develop a targeted family-based HIV-prevention intervention; 3) gain expertise in the collection and analysis of qualitative data that will inform the assessment of HIV/STI risk and subsequent intervention development; and 4) acquire advanced knowledge and skills in the design, methods and statistical analysis of behavioral intervention trials. Each research aim is directly linked with the training objectives; the research aims are: 1) to identify the HIV/STI risk reduction needs of youth on probation and understand logistic and institutional-cultural contextual factors of two probation centers to inform the development of a family-based HIV/STI intervention for JJS youth; 2) to develop with the probation community a family-based HIV/STI intervention for youth on probation by adapting a youth-only HIV/STI intervention for JJS youth and integrating formative data from Aim 1 and elements of efficacious family-based HIV/STI interventions; 3) to pilot test a family-based HIV prevention intervention with 36 families, randomized to intervention or delayed intervention conditions, to: a)examine the feasibility and acceptability of the intervention; b) establish estimated intervention parameters for a larger behavioral intervention trial; and c)explore the potential of the intervention to reduce youth HIV/STI risk behavior. The HIV/STI risk behavior of youth on probation is not just a correctional problem but also a public health concern. Empowered with the right tools and assisted by their families, youth on probation will be better equipped to make safer decisions that reduce the spread of HIV in their communities.